1. Field of the Invention
The present invention relates to novel polyester/silicone co-crosslinked materials, a process for the preparation thereof and to the use of such co-crosslinked polymers as a matrix containing an active principle (agent) for purposes of the controlled release of such active principle by simple erosion by hydrolysis of this matrix and/or by diffusion of the active principle through the matrix before or during erosion thereof.
2. Description of the Prior Art
In controlled-release systems of the above type, the release of the active principle, which is an inorganic, organic, biochemical or vegetable substance, depends on the nature of the active principle, the matrix and the erodible character of the matrix, which determine the release profile of the active principle.
The polymers which are biodegradable and, in particular, degradable by hydrolysis and which are already known to this art principally include polyethylene cyano esters, polyamides, polyurethanes, polyacetates, polylactones, polyanhydrides, polyorthoesters and polyesters.
The silicone polymers have also long been used, in crosslinked form, as a matrix within which an active principle is dispersed.
Numerous patents describe such matrix systems (for example, U.S. Pat. No. 4,053,580 and FR-A-2,560,768).
In this type of application, the silicones are not degradable by hydrolysis and are therefore not erodible.
In addition, for pharmaceutical and biological applications, the biocompatibility of the polymer is of fundamental importance.
For these applications, it is very difficult, and sometimes impossible, to remove undesirable products, such as catalysts and residual silicone polymers not integrated into the crosslinked product, from the crosslinked silicone polymer. Finally, the use of non-degradable crosslinked silicone generally prohibits the release of a macromolecular active principle.
The use of degradable polyesters of the polylactic or polyglycolic type of their copolymers was first described for the production of biodegradable surgical suture threads (U.S. Pat. Nos. 2,703,316 and 2,758,987 and FR-A-1,425,333.)
These polyesters have also been described as a matrix for the controlled release of active principles (EP-A-171,907, U.S. Pat. Nos. 4,011,312 and 4,272,920).
For controlled-release applications, the degradable polyesters have significant advantages:
(i) they are non-toxic, as are their degradation products produced by hydrolysis, and
(ii) to a certain extent, it is possible to modify the duration, the release profile of the active principle and the hydrolysis kinetics of the polymer, in particular by means of the choice of starting monomers, by means of the polymer chain length, its crystallinity, etc.
However, such polyesters have a glass transition temperature which is too high to permit the diffusion of a large number of active principles.
They frequently require high temperatures for the processing thereof which may be incompatible with the thermal stability of a large number of active principles.